Mapping a texture onto a fluid
I'm assuming the issue is that it's impossible/difficult to properly UV-unwrap a fluid, moving mesh?

2 solutions off the top of my head:


Use "Generated" as the Texture Coordinates, and then Use Box method on the Image node to blend the texture seams together.
If you need more control over the texture placement, use the UVProject modifier with a number of projector cameras in the scene. You might need to add an alpha feathered transition to the edge of the image manually in an external app. For an animated texture, you might need to blend it with an alpha mask image.